The prior art has addressed the notion of remotely enabling and/or disabling a circuit with radio frequency transponders. Philips Corp. has disclosed a vehicle immobilization technology that only permits a vehicle motor to start when a changeable code is passed from a tag in an ignition key to a circuit that is connected to the vehicle engine. The tag is not electrically connected to the circuit. In that technology, a complex tag reader is needed for each engine circuit that is to be enabled/disabled. The relatively simple tag in the key has to be in a specific proximity (location) with respect to the tag reader in order for the reader to access the code on the tag. Further, the tag reader will require power from some source associated with the enabled/disabled circuit. Because of the complexity, expense, and power requirements of the tag reader, this system is limited to enable/disable expensive circuits with on-board power.
RF tagging systems are also used to prevent theft in the retail industry, e.g. the sale of electronic equipment. It is estimated that retailers and manufacturers lose at least one per cent of their sales every year due to theft or `shrinkage`. The current approach to this problem is to place either an electronic article surveillance (EAS) tag, or an RF identification tag onto the item. These systems rely on either detecting the presence of an item within the proximity of a base station or the complete identifying of the tag. Both of these systems rely on the ability of the reader to detect a tag as it leaves a designated area. These systems basically are only able to activate an alarm when a stolen item is detected. If the system is defeated in some way, the stolen item, e.g., an electrical circuit will still be able to function. Therefore, a thief will have an incentive to defeat the system to pilfer the electronic equipment.